Abstract [en]

Clean water is necessary for human survival and there is a need for development of cheap and easy water purification techniques to use in emergency situations when there is no access to safe drinking water. Bacteria contaminated water can cause lethal diarrheal diseases and is globally the second most common cause of death among children less than five years of age.

Bacteria adsorbing filter paper made from cellulose could be an environmentally and economically sustainable alternative for disposable water purification filters. This thesis investigates the possibility to use polyelectrolyte multilayer modified cellulose pulp fibers and filter papers to adsorb and remove bacteria from water. The bacterial removal efficiency of the modified materials has been tested both in suspension and through filtration.

The surface modification provides the cellulose fibers with a positively charged surface that can attract and bind the negatively charged bacteria. The bacterial adsorption through electrostatic interactions makes it possible to remove bacteria, even when the pore size of the cellulose filters is larger than bacteria. Bacterial reduction tests shows that it is possible to remove over 99.9 % of the bacteria when filtering water through the modified materials. An increased amount of adsorbed cationic polyelectrolyte, polyvinylamine, resulted in an increased bacterial removal capacity. It has also been shown that the bacterial removal efficiency increases with an increased the amount of bacteria adsorbing materials in the filter.

The modified materials have been compared with a commercial product and the filtration efficiency has shown to be greater for the polyelectrolyte-modified materials, under the test conditions used in this thesis. Tests with natural water samples shows that it is important to use a filtration mode to remove particles from the water in combination with the bacterial adsorption, as the particles interfere with the bacterial adsorption.

Ek, Monica

Abstract [en]

Portable purification systems are easy ways to obtain clean drinking water when there is no large-scale water treatment available. In this study, the potential to purify water using bacteria adsorbing cellulose functionalized with polyelectrolytes, according to the Layer-by-Layer method, is investigated. The adsorbed polyelectrolytes create a positive charge on the cellulose surface that physically attracts and bonds with bacteria. Three types of cellulose material have been modified and tested for the bacterial removal capacity in water. The time, material-water ratio and bacterial concentration dependence, as well as the bacterial removal capacity in water from natural sources, have been evaluated. Freely dispersed bacteria adsorbing cellulose can remove greater than 99.9% of Escherichia coli from non-turbid water, with the most notable reduction occurring within the first hour. For turbid water, a filtering approach using modified cellulose fibers is desirable. This bacteria adsorbing cellulose does not leach any biocides, and it is an environmentally sustainable and cheap option for disposable water purification devices.

Ek, Monica

Abstract [en]

Water filtration is a popular way to remove particles and microorganisms from drinking water but is generally based on size exclusion of the particles. Bacteria can be modeled as small particles with a diameter of 1-2 µm, which is usually too small to be excluded by paper filters. In this article, commercial available paper filters have been surface modified by polyelectrolyte multilayer adsorption to create a positively charged filter that can trap the negatively charged bacteria through electrostatic interactions. The polyelectrolyte modified filters bind the bacteria to there surface and will thereby remove bacteria from the water instead of inactivated them through addition of biocides. The modified filters can remove more than 99.9 % of bacteria in water, depending on filter design, and has successfully been compared to a commercial cellulose water filter, based on the release of silver to inactivate bacteria. This cheap and easy modification of filter paper has potential to create disposable water purification filters that could be used in emergency situations to prevent outbreak of lethal diarrheal diseases.